Wireless communication systems enable users of User Equipment (UE) to communicate with other such users via one of a number of base stations and via one or a number of core networks. Typically, the UEs are mobile terminals, such as mobile (cellular) telephones and the like, although the term UE may also refer to generally stationary communication devices, such as laptop computers, web browsers, machine-type communication devices, and the like. In the following description the term user communication device is used, which is intended to cover any type of such user equipment (mobile and stationary).
In an active or connected state a user communication device is registered with the network and has a Radio Resource Control (RRC) connection with a base station so that the network knows to which base station (or cell thereof) the user communication device belongs and can transmit data to and receive data from the user communication device. Each user communication device also establishes a default Evolved Packet System (EPS) Bearer (i.e. an end-to-end dedicated communication path) from the user communication device to an endpoint beyond the base station, typically a gateway (such as a packet data network gateway—“PDN-GW” or “P-GW”—or the like), in the Enhanced Packet Core (EPC) network, or core network for short. An EPS Bearer, which is specific to the user communication device, defines a transmission path through the network and assigns an Internet Protocol (IP) address to the user communication device.
A Mobility Management Entity (MME) in the core network manages general mobility aspects of the user communication devices and ensures that connectivity is maintained with the user communication devices, for example as they are moving within the geographical area covered by the communication system (and/or as they are handed over between base stations of the communication system due to movement or changes in communication conditions). The MME also manages the various bearers associated with the user communication devices (such as an EPS bearer and/or the like) by controlling the other network nodes via which such bearers are provided. In order to do so, the MME exchanges Non-Access Stratum (NAS) signalling messages with the user communication devices (and/or the other network nodes) to manage the establishment of a communication session.
As part of the Long Term Evolution (LTE) of UTRAN (UMTS Terrestrial Radio Access Network) referred to as E-UTRAN, proximity-based services (ProSe) have been introduced, which make use of direct device-to-device (D2D) communication bearers directly between compatible user communication devices rather than indirect bearers provided from one user communication device, via a base station and the core network, to another user communication device (e.g. over a pair of EPS bearers). Thus, when a ProSe enabled user communication device is within the transmission range of (or served by the same base station as) another ProSe user communication device, they can communicate user data without the need to use core network resources. Such services can be achieved by establishing a special, “D2D”, bearer between the user communication devices in direct communication (or communication routed via their base station only) instead of their default or other conventional EPS bearers (which might be still used for other types of communications). This direct or locally routed communication could result in better utilization of the available resources, especially on the radio interface, where these are limited. Details of the ProSe functionality have been specified in the 3GPP Technical Report TR 23.703 document, the contents of which are incorporated herein by reference.
More recently the provision of a relay functionality, in the user communication device, using the ProSe functionality has been proposed to allow one user communication device (referred to as a “UE-Relay” or “UE-R”) to relay the signalling and the user data for another user communication device to and from the network, even if the other user communication device is not located within the network's coverage. In this case, the relayed user communication device can communicate with the network (both user plane and control plane data) via the UE-R thus accessing the same services as if the relayed user communication devices were served by a base station of the network.
In order to be able to benefit from ProSe services, a ProSe enabled user communication device performs a so-called discovery procedure (which can be done with or without network assistance/coverage). As part of this discovery procedure, each ProSe enabled user communication device transmits (e.g. periodically) a beacon for announcing itself to other such user communication devices in its proximity, and also listens for beacon transmissions by other devices. After two (or more) user communication devices have mutually discovered each other (e.g. they have received the other user communication device's beacon), they are able to start a ProSe communication session with each other.
The user communication device operating as a UE-R is able to relay traffic to one or more connected user communication devices via a (Relay) Packet Data Network (PDN) connection. In addition to this relay connection, the UE-R sends or receives (non-relayed) traffic for its own use (e.g. voice calls, Internet service, multimedia service, and/or the like).
In an exemplary scenario, a group of users (e.g. a team of Public Safety Officers at an emergency scene) may need to communicate with each other and/or with the network even when there is insufficient network coverage. In this case, one user can use his/her terminal as UE-Relay, while continuing to use it for his/her own needs as well. For example, the user of the UE-R may be using the following services: i) (group) voice services via an access point (gateway); and ii) video streaming from a remote server (e.g. an emergency scene monitoring server) via another (or the same) access point.
An access point typically comprises a gateway (e.g. a P-GW mentioned above) and can be identified by its associated Access Point Name (APN). In order to ensure that an appropriate level of service (e.g. a desired data rate) can be provided for each user in the communication network, the network operator assigns various parameters that determine an aggregate maximum bit rate (AMBR) that can be provided to the users (subscribers) in the network per subscriber and per access point. Specifically, for each subscriber, the Home Subscriber Server (HSS) holds an associated “HSS_APN-AMBR” parameter (per APN) and an “HSS_UE-AMBR” parameter, forming part of the user's subscription data.
The HSS_APN-AMBR (APN Aggregate Maximum Bit Rate) parameter for a particular (subscriber's) user communication device limits the non-guaranteed aggregate bit rate across all PDN connections by that user communication device via a particular APN. The actual “APN-AMBR” parameter to be used (enforced) by the given access point (e.g. P-GW) is provided by the MME based on subscription data obtained from the HSS.
The HSS_UE-AMBR (UE Aggregate Maximum Bit Rate) parameter for a particular (subscriber's) user communication device limits the total traffic of that user communication device on uplink and downlink (via the serving base station). The actual “UE-AMBR” parameter to be used (enforced) by the serving base station is provided by the MME based on subscription data obtained from the HSS. Specifically, the MME computes the UE-AMBR parameter such that it equals the smaller of the sum of all HSS_APN-AMBR parameters of active APNs and the HSS-UE-AMBR parameter. This is further illustrated in the 3GPP TS 23.401 standard, the contents of which are incorporated herein by reference. The MME transmits the calculated UE-AMBR parameter to the serving base station, which base station is thus able to allow/discard data traffic for the user communication device in accordance with the UE-AMBR parameter. This is further illustrated in the 3GPP TS 36.413 and TS 36.300 standards, the contents of which are incorporated herein by reference.
Thus traffic sent/received by a particular user communication device in excess of the bit rate indicated by the UE-AMBR parameter may get discarded by a rate shaping function of the base station serving that user communication device, and traffic exceeding the bit rate indicated by the applicable APN-AMBR parameter may get discarded by a rate shaping function of the corresponding APN. The UE-AMBR parameter and the APN-AMBR parameter are applicable across all non-Guaranteed Bit Rate (non-GBR) bearers of a particular subscriber (i.e. a user communication device associated with that subscriber).